Journal of Nematology 38(1):168–171. 2006. © The Society of Nematologists 2006. Control of the Oriental Fruit Moth, Grapholita molesta, Using Entomopathogenic Nematodes in Laboratory and Fruit Bin Assays E. Riga,1 L. A. Lacey,2 N. Guerra,1 H. L. Headrick2 Abstract: The oriental fruit moth (OFM), Grapholita molesta (Busck), which is among the most important insect pests of peaches and nectarines, has developed resistance to a wide range of insecticides. We investigated the ability of the entomopathogenic nematodes (EPN) Steinernema carpocapsae (Weiser), S. feltiae (Filipjev), S. riobrave (Cabanillas et al.), and Heterorhabditis marelatus (Liu and Berry) to control OFM under laboratory and fruit bin conditions. At a dosage of 10 infective juveniles (IJ)/cm2 in the laboratory, S. carpocapsae caused 63%, S. feltiae 87.8%, S. riobrave 75.6%, and H. marelatus 67.1% OFM mortality. All four nematode species caused significant OFM larval mortality in comparison to the nontreated controls. Steinernema feltiae was used for the bin assays due to the higher OFM mortality it caused than the other tested EPN species and to its ability to find OFM under cryptic environments. Diapausing cocooned OFM larvae in miniature fruit bins were susceptible to IJ of S. feltiae in infested corner supports and cardboard strips. Treatment of bins with suspensions of 10 or 25 S. feltiae IJ/ml water with wetting agent (Silwet L77) resulted in 33.3 to 59% and 77.7 to 81.6% OFM mortality in corner supports and cardboard strips, respectively. This paper presents new information on the use of EPN, specifically S. feltiae, as nonchemical means of OFM control. Key words: Biological control, cardboard strips, fruit bins, Grapholita molesta, entomopathogenic nematodes, Heterorhabditis marela- tus, oriental fruit moth, Steinernema carpocapsae, S. feltiae, S. riobrave, wetting agent. Oriental fruit moth (OFM), Grapholita molesta, a na- 1990). Efficacy of several EPN species has been demon- tive insect of China, has spread throughout the world strated against a wide variety of insect pests (Kaya and and is considered the most important insect pest of Gaugler, 1993; Gaugler, 2002), including codling peaches. Since its introduction into North America, moths, Cydia pomonella (L.), in both orchards and fruit OFM has become a serious pest of peaches, nectarines, bins (Kaya et al., 1984; Unruh and Lacey, 2001; Lacey et apricots and apples (Rothschild and Vickers, 1991). It al., 2005). Several species in the Tortricidae, in which was first detected in the eastern United States in 1913, genus G. molesta belongs, use cryptic habitats during reached California by 1942, and is now found in all some of their life stages. Full-grown OFM larvae over- peach-growing areas of the United States and Canada winter in cocoons in bark crevices, orchard trash, (Rothschild and Vickers, 1991). The moth is difficult to weeds, ground cover, and fallen fruits. The OFM larvae control because it has several generations throughout pupate in early spring, and four to five generations can the growing season and has developed resistance to exist per year (Kanga et al., 1999). organophosphate insecticides with cross-resistance to Cryptic habitats used by insects are also good habitats carbamates (Kanga et al., 1997, 1999). In addition, for EPN applications (Kaya and Gaugler, 1993; Gaugler growers who have switched to pyrethroids are also con- at al., 1997). Recently, Lacey et al. (2005) used EPN for cerned that OFM might develop resistance to this class control of overwintering codling moth in fruit bins by of insecticides (Pree et al., 1998). incorporating cardboard strips and wooden corners to Incorporation of an effective biological control agent mimic cryptic environment. In addition, they used a in the management of OFM might lead to reduction of wetting agent, Silwet L77, to assist the penetration of insecticide use against this pest and alleviate the selec- EPN into codling moth hibernacula, and a humectant tive pressures that cause the insect to develop resis- to prevent EPN desiccation. tance. In addition, the use of biological control agents OFM control could be effective if EPN were used to in lieu of insecticides could minimize human exposure target the overwintering cocooned larvae found in cryp- to synthetic pesticides and eliminate the need for buffer tic habitats. The purpose of this study was to determine zones in urban areas and sensitive habitats adjacent to the ability of entomopathogenic nematodes to infect orchards. and kill OFM in laboratory and miniature fruit bin as- Entomopathogenic nematodes (EPN) have the po- says. This paper presents new information on the use of tential to be effective biological control agents due to EPN for control of cocooned OFM larvae. their broad host range, host-seeking abilities, high viru- lence, and safety for vertebrates and plants (Poinar, Materials and Methods Test insects: OFM larvae used in experiments were Received for publication December 15, 2005. reared on soy-wheat germ-starch artificial diet (Toba 1 Washington State University, IAREC, 24106 N. Bunn Rd., Prosser, WA 99350. and Howell, 1991) under diapausing conditions (pho- 2 Yakima Agricultural Research Laboratory, USDA-ARS, 5230 Konnowac Pass toperiod of 12:12 [L:D], 21°C, 41–45% RH) in a colony Rd., Wapato, WA 98951. The authors thank Lorraine Seymour for assistance with assays and bin tests, maintained at the Yakima Agricultural Research Labo- Pauline Anderson for rearing OFM larvae, and Don Hostetter and Steve ratory (YARL) in Wapato, Washington. Arthurs for review of the manuscript. E-mail: [email protected] Test nematodes: Steinernema feltiae (Umea strain), S. car- This paper was edited by Patricia Stock. pocapsae (Sal strain), S. riobrave (originally obtained 168 Oriental Fruit Moth Control: Riga et al. 169 from H. Kaya, University of California, Davis) and Het- supports that had been removed from bins were placed erorhabditis marelatus (originally obtained from R. Berry, on rearing trays that contained diapause-destined ma- Oregon State University, Corvallis, OR) were used in turing OFM larvae. Full-grown larvae were allowed to this study. Infective juveniles (IJ) used were produced spin cocoons in the supports several days prior to test- in wax moth, Galleria mellonella (L.), according to pro- ing. After formation of cocoons, the corner supports cedures described by Kaya and Stock (1997), stored at were stored in a 12°C ± 0.5°C incubator until they were 10°C in moist sponges, and used within 2 wk of pro- used for testing. On the day of the test, they were in- duction. Quality control of test nematode infectivity was serted into the corners of the fruit bins with wood conducted for each experiment against diapausing co- screws and an electric drill. The number of OFM larvae 2 cooned OFM larvae in 15.2-cm perforated cardboard per corner support was variable. The average number strips (double-faced, B flute, Weyerhaeuser, Tacoma, of OFM larvae in controls was 33.4 (ranged from 7–45), 2 WA) using 152 IJ in 1 ml water (10 IJ/cm , 4 strips per in tests with S. feltiae (10 IJ/ml) was 104 (ranged from treatment and control) and methods prescribed by 62–139), and in tests with S. feltiae (25 IJ/ml) was 87 Lacey and Unruh (1998). The treated strips were (ranged from 51–169). placed in filter-paper-lined petri dishes (9-cm-diam.), Similarly, perforated cardboard strips (41.0-cm long incubated for6dat25°C ± 1.7°C, and then assessed for by 1.9-cm wide, double-faced, C flute) were infested mortality. Quality control was performed directly on with diapausing OFM. The number of OFM larvae per OFM as the mortality observed in OFM strips was very strip was variable. In control strips the average number close to that of codling moth larvae reported in studies of OFM larvae was 32.6 (ranged from 7–62), in tests conducted by Lacey et al. (2005). We used 25°Casthe with S. feltiae (10 IJ/ml) the average was 30 (ranged optimal temperature for testing EPN, as this tempera- from 7–64), and in tests with S. feltiae (25 IJ/ml) the ture can be obtained in fruit-packing houses where bins average was 37 (ranged from 6–86). The infested card- would be stored for the first 24 hr following treatment board strips were placed in spaces in one corner of each (Lacey et al., 2005). of the bins. The space was made by placing a strip of Susceptibility of OFM to EPN: Steinernema carpocapsae, S. Plexiglas (24.-m long × 2.5-cm wide × 6.4-mm thick) feltiae, S. riobrave, and H. marelatus IJ were used to treat between one of the corner supports and adjacent walls cocooned larvae or pupae in 15.2-cm2 perforated card- 2 cm from the corner. board strips using the procedures described by Lacey The miniature bins were treated by immersing them and Unruh (1998). Five strips were used for each EPN in a deep, straight-sided wheelbarrow (Rubbermaid species and control. The strips were treated with 1 ml of water or 1 ml of water containing 152 IJ (10 IJ/cm2) farm cart, Fairlawn, OH) filled with 170.3 liters of water placed in filter-paper-lined-petri dishes, incubated for 6 to within 2.8 cm of the top. Two concentrations (10 and dat25°C ± 1.7°C, and then assessed for mortality. Al- 25) of S. feltiae IJ/ml of water were used. In all tests, though we aimed for 20 OFM per cardboard strip, the immersion time in the tank was 1 min. Water used in number was variable. In the control strips, the average the experiments was nonchlorinated well water (20.6°C number of OFM larvae per strip was 13.2 (ranged from ± 0.5°C; pH 7.5).